Best? No. Most iconic and important? Yes. But if you look at it, 'almost every Zelda game is not at all true." There is:
-ALTTP
-OOT
-WW
-TP
-SS
5 games! out of 16!
now, OOA and OOS have a Master Sword too, but in name only. there is no plot relevence and its position in an alternate dimension makes it likely that it is just another culture's similar weapon. Also, there is Four Swords Anniversary Edition, in which it can be unlocked, but that is merely an add-on to your Four Sword. In this case, 'Master Sword' is synonymous with beam-shooting sword, implying that perhaps legends of the hero of SS have created the term 'Master Sword'. Plus, there is a 'REalm of Memories' so the Master Sword could be considered to have more of a dream-like presence in the game.